The project in progress explores the relationship of biogenic amines to certain endocrine tumors and tumors with endocrine function in two ways. Firstly, the amine metabolizing enzyme, histaminase (diamine oxidase), which is found in medullary thyroid carcinoma, is being extensively studied in this tumor, and in other tumors which may be embryologically related. Methods for rapid and high degree purification of the enzyme have been developed. Purified histaminase from human placenta is being compared (substrate specificity, electrophoretic mobility, amino acid content, and antigenicity) to histaminase in medullary thyroid carcinoma, small cell carcinoma of the lung, human kidney and intestine, and rat thymus, intestine and adrenal glands. Through such comparisons it is hoped that the expression of this enzyme activity by certain tumors will be better understood. Secondly, the effect of amines such as dopamine, norepinephrine and serotonin on peptide hormone release from tumors capable of endogenous synthesis of these amines is under investigation. In vivo and in vitro studies of calcitonin release from medullary thyroid carcinoma tissue are being used for this purpose. Release of this hormone under conditions of added amine precursors in the presence and absence of blockade of biogenic amine synthesis is being explored. BIBLIOGRAPHIC REFERENCES: Baylin, S.B.: Histaminase (diamine oxidase) activity in human tumors: An expression of a mature genome. Proc. Nat'l. Acad. Sci (USA) 74-883, 1977. Shakir, K.M.M., Margolis, S., and Baylin, S.B.: Localization of histaminase in rat small intestinal mucosa: Site of release by heparin. Biochem. Pharmacol., In press, 1977.